Chemical building blocks self-assemble to form a catalyst

This fact makes them ideal candidates to replace expensive platinum catalysts currently used in the preparation of hydrogen fuel cells, says Dr. Timothy Cook, professor of chemistry at the University of Buffalo

[Translation by Dr. Nachmani Moshe]

What's better than platinum? In the field of hydrogen fuel cells, the answer may be cobalt porphyrins. These self-assembling molecules - and highly effective in accelerating the chemical reaction required to produce energy from hydrogen and oxygen - could be the next advance in the field of alternative energy.

 

The compounds are self-assembled in the lab from Lego-like building blocks and designed to fit together. It is a 'mix and bake' type of technology: the scientists add the building blocks to the powder, mix them together and apply heat. Over time, the building blocks fit together in the appropriate locations to create the final product. The material is cheap and simple to produce in large quantities. This fact makes them ideal candidates for replacing expensive platinum catalysts currently used in the preparation of hydrogen fuel cells, says Dr. Timothy Cook, professor of chemistry at the University of Buffalo.

This kind of technology could, in the near future, allow companies to reduce the prices of hydrogen-powered cars, which would make it possible to expand the customer base of environmentally friendly vehicles. Cheap fuel cells could, in addition, encourage the development of other energy devices based on hydrogen, such as power generators for backup situations. Hydrogen is considered a clean energy source since fuel cells only emit water as a byproduct. "In order to reduce the price of hydrogen vehicles and make them a practical option for a wider audience, we need a catalyst that will be cheaper than the platinum catalysts," says the lead researcher. "The catalyst we developed is able to self-organize in large quantities. The catalyst itself contains ruthenium and cobalt - metals that are much cheaper than platinum - and still, it works well and even better than commercially available platinum catalysts that we also tested for comparison." The research findings have long been published in the scientific journal Chemistry: A European Journal.

Researcher Cook's lab specializes in molecular self-assembly, a valuable process used to make new materials. "When I think about molecular self-organization, I always imagine building blocks of the Lego game," says the lead researcher. "You have in your hand building blocks that are designed to fit together, like parts of an assembly. Our building blocks do more than that - they are attracted to each other, and when you bring them closer together and add energy, they connect to each other themselves. "Self-assembly is an efficient method for preparing complex molecules. Normally, in order to synthesize a new material, you have to put it together piece by piece, an expensive and time-consuming process. Molecular self-organization is a fast process - it is actually a one-step process." The new catalyst consists of two flat porphyrin cobalt molecules, which are stacked together one on top of the other like a sandwich, and connected by the metal ruthenium." In order to synthesize the final product, the researchers designed porphyrins and connectors with chemical properties that ensure they will attach to each other in the appropriate locations. Next, the researchers mixed a solution of the porphyrins with the compounds and then applied heat. Within two days, the parts organized themselves to create the required final product.

Similar to the platinum catalyst they plan to replace, the cobalt porphyrins accelerate a chemical reaction used in the development of hydrogen fuel cells called oxygen reduction. During this reaction, an oxygen molecule splits into two separate oxygen atoms that can reconnect with hydrogen atoms to form water - while receiving energy. Scientists have known for a long time that porphyrins are effective in capturing and splitting oxygen: in the human body itself, iron-based versions of porphyrins are responsible for converting the oxygen we breathe into water, emitting energy that the body uses, explains the lead researcher. At the same time, the development of artificial porphyrin structures that function as catalysts has so far been challenging, he adds. The preparation process of these compounds is usually expensive, and involves many steps while obtaining a small amount of the final product. Self-assembly solves these problems: the research team was able to produce 79 grams of porphyrin cobalt from every 100 grams of starting material - a recovery much better than the recovery that other laboratories reported for similar materials, recoveries at the single percent level. In addition, the research team was able to synthesize and test the ruthenium connectors of different lengths so that they would be suitable for sensitive tuning of the electrochemical properties of the compound in order to reach the ideal catalyst. "It is really rewarding to work on the basic chemistry of this project, research that could have a significant impact in the field of green energy," says one of the researchers. "Using self-assembly methods, we were able to prepare cheaper materials within forty-eight hours, without requiring challenging purification steps that require a lot of time, steps that are common in other methods for the synthesis of new materials."

Article Summary

The news about the study

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• A cheap and clean method to produce hydrogen for fuel cells